Telescopic props

ABSTRACT

A telescopic prop with an outer member and first and second concentric inner members which inner members are disposed within said outer member and are longitudinally displaceable. The first inner member is extendable and retractable hydraulically whereas the second inner member is extendable hydraulically but retractable non-hydraulically. Each inner member has a piston facing a chamber chargeable with hydraulic pressure fluid and two spring-biased non-return valves are operably disposed between the chambers, one valve opening in a direction between the chamber associated with the piston of the first inner member and the chamber associated with the piston of the second inner member and the other valve opening in the opposite direction.

nite States atent Plester et al.

[151 3,66A11 5] Ar. 1,1972

[ TELESCOPIC PROPS I Gewerkschaft Eisenhutte Westfalla, Westfalia, Germany [22] Filed: Oct. 10,1969

[21] App1.No.: 865,355

[73] Assignee:

[30] Foreign Application Priority Data June 21, 1969 Germany .1. ..P 19 31 627.9

[56] References Cited UNITED STATES PATENTS 3,252,680 5/1966 Lee etal. ...92/52 2,172,117 9/1939 Beaufort et a1. ..92/51 2,378,409 6/1945 Joy ....9l/422 2,517,153 7/1950 Wood .,..91/l69 2,813,515 11/1957 Curtis ..92/5l 3,426,649 2/1969 Koppers ..9 H422 Primary Exdminer-Everette A. Powell, Jr. Assistant Examiner-Clemens Schimikowski Attorney-Sughrue, Rothwell, Mion, Zinn 8: Macpeak [5 7] ABSTRACT A telescopic prop with an outer member and first and second concentric inner members which inner members are disposed within. said outer member and are longitudinally displaceable. The first inner member is extendable and retractable hydraulically whereas the second inner member is extendable hydraulically but retractable nonhydraulically. Each inner member has a piston facing a chamber chargeable with hydraulic pressure fluid and two spring-biased non-return valves are operably disposed between the chambers, one valve opening in a direction between the chamber associated with the piston of the first inner member and the chamber associated with the piston of the second inner member and the other valve opening in the opposite direction.

1 Claims, 2 Drawing Figures PATENTEDAPR 18 I972 3,656,411

FIGZ.

INVENTOR ATTORNFY BACKGROUND TO THE INVENTION Telescopic props are known which have an outer member within which is disposed two concentric inner members extendable and retractable relative to the outer member. The first inner member, disposed between the outer member and the second inner member, has a piston provided with a bore to allow pressure fluid to act on a piston of the second inner member. Pressure fluid flows through this bore when the first inner member has been moved fully outwards to thereby move the second inner member outwards until the prop is secured in the desired manner. In practice the second inner member is only able to move outwards by a certain amount.

In the process of retraction, the first inner member is retracted hydraulically and a rising pressure will form underneath the piston of the first inner member. This pressure is transmitted through the bore in the piston to act upon the piston of the second inner member. Thus, as the first inner member is being retracted the second inner member is being extended. For this reason the complete retraction of the prop cannot be effected until sufficient time has elapsed to allow the second inner member to move inwards under its own weight or to allow the second member to be moved inwards by additional mechanical devices. I

A general object of this invention is to overcome the aforementioned disadvantage and in particular to ensure that the second inner member will not move outwards when the first inner member is being retracted.

SUMMARY OF THE INVENTION According to the present invention there is provided a telescopic prop comprising:

a. an outer member,

b. a first inner member disposed within said outer member and mounted for longitudinal displacement relative to said outer member,

c. a second inner member disposed within said first inner member and mounted for longitudinal displacement relative to said first inner member,

d. a first piston formed at the inner end of the first inner member, a second piston formed at the inner end of the second inner member f. a first chamber chargeable with hydraulic pressure fluid and disposed between said outer member and said first piston,

g. means for admitting hydraulic pressure fluid into said first chamber,

h. a second chamber chargeable with hydraulic pressure fluid and disposed between said first and second pistons,

i. a first spring-biased non-return valve operably disposed to open in'a direction from the first chamber to the second chamber, and

j. a second spring-biased non-return valve operably disposed to open in a direction form the second chamber to the first chamber.

According to a further feature of the invention the spring force of the first valve is greater than the spring force of the second valve. The valves are preferably disposed in a housing carried by the first piston. The second piston is then recessed to receive the housing when the first and second pistons are disposed adjacent one another,

The invention may be understood more readily, and other features of the invention may become more apparent, from consideration of the following description.

BRIEF DESCRIPTION OF DRAWING A constructional embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawing, wherein:

FIG. 1 is a vertical section through a telescopic prop made in accordance with the invention; and

FIG. 2 is a view corresponding to FIG. 1, but on a larger scale showing the piston of the first inner member and the construction of the non-return valves.

DESCRIPTION OF PREFERRED EMBODIMENT As shown in FIG. 1, a hydraulically operated telescopic prop has a cylindrical outer member 12 within which is disposed a first cylindrical inner member 3. A second inner member 2 is in turn disposed within the member 3. An annular chamber 13 is provided between the inner member 3 and the outer member and is used in an operation known as robbing.

The inner member 3 is provided with a piston 4 at its innermost end and the piston 4 is formed with a housing 10 containing non-return valves 5, 6. The lower end of the member 12 is provided with a base and a chamber ,8 is formed between the base and the piston 4. A bore 14 is provided in the base to allow the chamber 8 to be charged with hydraulic pressure fluid. The member 2 likewise has a piston 9 at its innermost end and a chamber 7 is provided between the pistons 4, 9. A recess 11 in the piston 9 can receive the valve housing 10 when the pistons 4, 9 lie adjacent one another.

FIG. 2 shows the construction of the non-return valves 5, 6 which are of conventional design. The valve 6 has a valve element in the form of a ball 15 which is urged by a compression spring against a seating 16. The valve 5 has a valve element in the form of a ball 18 which is urged against a seating 19 by means of a plunger acted upon by a compression spring 17. The force of thespring 17 is greater than that of the spring of the valve 6. The valves 5, 6 act in opposition to one another with the valve 5 opening in the direction from chamber 8 to chamber 7 and the valve 6 opening in the direction from chamber 7 to chamber 8.

The operation of the prop is as follows:

If pressure fluid is conveyed through the bore 14 and into the chamber 8, the members 2, 3 will move together outwardly of the member 12 and at this stage the ball 15 of the valve 6 is pressed against its seating 16 so the valve 6 is closed. The valve 5 likewise remains closed, since the spring 17 urges the ball 18 against its seating 19. When the member 3 has been moved completely outwardly of the member 12 to the maximum extent pressure will build up in the chamber 8 under the piston 4 until the pressure is sufficient to overcome the force of the spring 17 and lift the ball 18 from its seating 19 to thereby open the valve 5. Pressure fluid now flows into the chamber 7 underneath the piston 9 if the inner member 2 is allowed to extend it will move outwardly from the inner member 3. The prop can now be set in its roof supporting position. When it is desired to retract the prop pressure fluid is conducted to the chamber 13 used as a robbing aid via a bore 20 and the pressure fluid in the chamber 8 is allowed to discharge so that the pressure therein falls to a minimum value. The piston 4 now moves downwardly as the member 3 is retracted. During this process, the valve 5 will be closed and a pressure head will be established in the chamber 8, owing to the descending movement of the piston t. The rising pressure in the chamber 8 acts against force of the spring 17 of the valve 5, but the force of the spring 17 is such that it is sufficient to overcome this pressure in the chamber 3 to keep the valve 5 in its closed position. Thus, no pressure fluid can enter the chamber 7 while the member 3 is retracted as occurred hitherto. The valve 6 also remains closed when the member 3 is being retracted and only opens after the termination of this process, when there is no longer any pressure in the chamber 8 underneath the piston 4 to allow relief of any pressure in chamber 7. At this stage when the member 3 is fully retracted the weight of the member 2 causes the pressure in the chamber 7 to lift the ball 15 from its seating 16. When the valve 6 opens the inner member 2 can thus retract under its own weight or alternatively mechanical auxiliary devices can be utilized to retract the member 2 more quickly.

We claim:

hydraulically, said prop comprising:

a. an outer member,

b. a first inner member disposed within said outer member and mounted for longitudinal displacement relative thereto;

0. a second inner member disposed within said first inner member and mounted for longitudinal displacement relative thereto.

d. a first piston formed at the inner end of the first inner member; said first piston including only two passages capable of receiving valves;

e. a second piston formed at the inner end of the second inner member;

f. a first chamber disposed between the outer member and said first piston g. means at the base of said outer member for admitting hydraulic pressure fluid into the first chamber to extend the first and second members together;

h. a second chamber disposed between said first and second pistons;

i. a third chamber disposed between the first inner member and the outer member;

j. means for admitting hydraulic pressure fluid into said third chamber to retract the first and second members together;

k. a first spring-biased non-return valve operably disposed in one of said two passages and between the first and second chambers and adapted to open in a direction from the first chamber to the second chamber when the first inner member has been fully extended to allow pressure fluid to enter the second chamber and extend the second inner member beyond the first inner member; and

l. a second spring-biased non-return valve operably disposed in the other of said two passages and between the first and second chambers and adapted to open in a direction from the second chamber to the first chamber when the first inner member has been fully retracted to permit pressure fluid to be discharged from the second chamber to allow the second inner member to retract;

rn. wherein the spring force of the first valve is considerably greater than that of the second valve for preventing pressure fluid from entering said second chamber during retraction of said first inner member;

n. said first and second valves being disposed in a single housing carried by the first piston and the second piston is provided with a recess which can receive said housing when the first and second pistons are brought together. 

1. A telescopic prop which can be extended and retracted hydraulically, said prop comprising: a. an outer member; b. a first inner member disposed within said outer member and mounted for longitudinal displacement relative thereto; c. a second inner member disposed within said first inner member and mounted for longitudinal displacement relative thereto; d. a first piston formed at the inner end of the first inner member; said first piston including only two passages capable of receiving valves; e. a second piston formed at the inner end of the second inner member; f. a first chamber disposed between the outer member and said first piston g. means at the base of said outer member for admitting hydraulic pressure fluid into the first chamber to extend the first and second members together; h. a second chamber disposed between said first and second pistons; i. a third chamber disposed between the first inner member and the outer member; j. means for admitting hydraulic pressure fluid into said third chamber to retract the first and second members together; k. a first spring-biased non-return valve operably disposed in one of said two passages and between the first and second chambers and adapted to open in a direction from the first chamber to the second chamber when the first inner member has been fully extended to allow pressure fluid to enter the second chamber and extend the second inner member beyond the first inner member; and l. a second spring-biased non-return valve operably disposed in the other of said two passages and between the first and second chambers and adapted to open in a direction from the second chamber to the first chamber when the first inner member has been fully retracted to permit pressure fluid to be discharged from the second chamber to allow the second inner member to retract; m. wherein the spring force of the first valve is considerably greater than that of the second valve for preventing pressure fluid from entering said second chamber during retraction of said first inner member; n. said first and second valves being disposed in a single housing carried by the first piston and the second piston is provided with a recess which can receive said housing when the first and second pistons are brought together. 